The Public Switched Telephone Network (PSTN) is the backbone for providing telephony services to business and individuals in the United States. In addition to telephony, the PSTN is increasingly being relied upon to carry data traffic. In fact, data traffic on the PSTN has become so heavy that it has surpassed the amount of voice traffic. One way in which the PSTN has evolved to meet these demands is to employ Digital Subscriber Lines (DSLs). The DSLs include Integrated Services Digital Network (ISDN) lines and more recently Asymmetrical Digital Subscriber Lines (ADSL). ADSL is in many ways preferred over other DSLs since ADSL does not require the provisioning of any new lines but instead can be executed over a single twisted-wire pair, such as an existing telephone line.
In addition to Plain Old Telephone Services (POTS), an ADSL system also permits full-duplex and simplex digital services with data rates from about 1.5 Mbits/second to 7 Mbits/second. An ADSL system uses a spectrum from about 26 kHz to 1.1 MHz for broadband data transmission and leaves the spectrum from about DC to 4 kHz for POTS. An ADSL system is more than capable of providing video-on-demand capability, video conferencing, data file transfer capability and can provide all of this capability simultaneously with POTS. For additional information, reference may be made to American National Standards Institute Standard ANSI-T1.413-1995 which describes an ADSL system and an interface between a telecommunications network and a customer's installation and which is incorporated herein by this reference.
While ADSL can be executed over existing telephone lines, not all telephone lines are capable of carrying ADSL traffic. Consequently, when a customer orders ADSL service, a technician is typically dispatched to the location to test the line. One way in which a technician tests the line is by trying to establish communications between an ADSL transceiver located at the customer's premises with an ADSL transceiver located at a central office. If the ADSL transceivers are able to communicate with each other to a satisfactory degree, then the ADSL services may be deployed at the customer's premises.
The need to dispatch a technician to the customer's premises before deploying ADSL services is a great inconvenience and has a high cost. The need to test the line places a great burden on the technicians who must be dispatched to the customer's premises. For areas that may have thousands if not millions of potential ADSL customers, using technicians to test the line at each customer's premises is impractical. In addition to the enormous cost associated with the technicians, the need for an ADSL transceiver at the customer's premises also presents a substantial expense. This expense is often incurred by the customer before the customer even knows if ADSL are available. Even if the cost of the ADSL transceivers are absorbed by the service provider, the transceivers still require an outlay of capital before ADSL services can be deployed.
Other methods of qualifying lines for digital services involve testing that occurs at the central office. U.S. Pat. Nos. 5,864,602, 5,978,449, and 6,084,946, which are incorporated herein by reference, describe various ways of qualifying lines for digital service. These methods generally involve applying an AC test signal and then measuring a tip-to-ring capacitance of a wire pair. Some of the methods described in these patents involve additional measurements, such as measuring a second impedance of the wire pair at another frequency. Based on these measurements, the line is qualified to receive digital services if the measurements are within prescribed limits. While these methods avoid the need to dispatch a technician to the customer's premises, these methods still require testing to occur at the central office for each line.
The testing of lines to qualify them for new services is further complicated in that more than one company may provide the digital services over any given line. Whereas the incumbent local exchange carrier (LEC) would traditionally provide all local services to the lines within its region, the opening up of the local loops to competition now makes it possible for competitive local exchange carriers (CLEC) to not only offer local telephony service but also to offer peripheral services, such as digital services. Providing all of these companies access to all of the lines in order to test them for potential serve is impractical.
A need therefore exists for improved systems and methods for qualifying loops for ADSL services.